This invention relates to a method for the manufacture of a diaphragm possessing a rubber layer on both or either of the opposite surfaces of a substrate fabric and an apparatus for performing the method.
The present invention is described with reference to a diaphragm 3 possessing two rubber layers 2 severally on the opposite surfaces of a substrate fabric 1 as illustrated in FIG. 2. The present invention is equally applicable to a diaphragm possessing one rubber layer on only one of the surfaces of a substrate fabric. The material for the substrate fabric 1 is generally a woven fabric of fibers such as of cotton, nylon, rayon, or polyester and the material for the rubber layer is NBR, EPDM, CR, or CO (epichlorohydrin rubber).
The procedure heretofore followed in the manufacture of such a diaphragm is as illustrated in FIG. 27.
A substrate fabric 1 having adhesive agent applied thereof is paid out, led in between compression rolls 102 of a calendering machine 101, and subjected to one-surface topping twice therein to produce a fabric-containing sheet 10. The fabric-containing sheet 10 is cut by a cutting device (not shown) to a prescribed length (generally not less than 1 m) and the cut pieces of the sheet are piled up. The pieces of the fabric-containing sheet 10 are perforated one by one with a punch 104 and a die 103 to produce circular materials 105. The circular materials 105 are set one each in circular depressions 108 in a lower mold 107 of a press vulcanizer 106 and subjected to press vulcanization. The circular materials 105 thus press vulcanized are given secondary vulcanization when necessary and then punched one by one with a punching device 111 to produce diaphragms 3. The diaphragms thus produced are visually tested for diameter and wall thickness, packaged, and shipped. If the substrate fabric is found to have any defective portion due to insufficient application of adhesive agent, for example, it has been customary for that defective portion to be marked by tying a yarn to the lateral part of the substrate fabric so that the defective portion will be removed while the fabric-containing sheet 10 resulting from the topping of the substrate fabric is being cut into separate pieces.
The procedure described above has entailed the following problems.
(a) The fabric-containing sheet produced by the calendering machine has a width (at least 1 m.) large enough for a plurality (at least 10) of diaphragms (generally of a unit diameter of not more than 10 cm) to be obtained in a row in the direction of width of the sheet. Thus, the supply of the rubber material and that of the fabric cannot be easily automated. Further, in the step of press vulcanization, the circular materials must be inserted into and removed from the press vulcanizer manually one by one. The procedure as a whole calls for a large number of steps and the operation does not prove desirable from the standpoint of safety.
(b) It is difficult to give to the fabric-containing sheet produced by calendering a uniform thickness both in the direction of travel and in the direction of width. The fabric-containing sheet, therefore, is liable to include portions deviating in thickness from the specified range. If the substrate fabric happens to include a defective portion, the section of the substrate fabric wholly covering the defective portion and extending throughout the entire width of the substrate fabric must be cut away, degrading the yields of materials used as a whole.
(c) Since the production requires use of the calendering machine, the entire production equipment is quite voluminous and the operation thereof calls for use of a large motive force.